Iv ae eenneefelt



I. RENNERFELT.

ELECTRIC FURNACE.

APPLICATION mso MAL 3. 192x.

1,428,908, PatentedSept. 12', 1922.

Im/enfor.-

Wifnesqes:

Patented Sept. l2, 1922.

UNITED STATES PATENT OFFICE.

ELECTRIC FURNACE.

Application led March 3,

To allwlwm it 'may concern.'

Beit known that I, Ivan RENNERELT, acitizen of the Kingdom of Sweden, and resident of Djursholm, in the county of Stockholms Lan and Kingdom of Sweden, Vhave invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification. v

My invention` relates to improvements in the construction of an electrically heated Crucible furnace and has for its ob'ects'to provide a furnace especially suta le for utilizing a ,granulated resistance for heating a Crucible, the muie of a heat-treating lfurnace or some other hollow or solid object.

It is previously well known in the art,

that a crucible may be heated by surroundw ing it by' for instance crushed coke or graphite and passing an electric current through said coke or graphite, which acts as a resistance generating a. considerable amount of heat in the space surrounding the Crucible. It has, however, heretofore not been possible to successfully use twoor threephase current in suchfurnaces. This isa disadvantage, especially if the power required is not rather small, because in most cases an unbalanced sin lephase load is not permitted on a polypghaseY distribution system. 1

It is also generally necessary to use a rather low voltage or to use an external resistance yin series with the is impractical for man the said resistance with a comparativelyv small cross section in connection with a. substantial length as required for using a voltage as commonly obtainable.

In order to attain the objects of my invention I propose to arran e the heating resistance as strings alongsi e of the crucible or mule. If the furnace is phase current, the number of resistance strings should be three, separated from each other by suitable means.

lt is also possible to changethe number of phases from 3 to Z by a special transformer,

as is well known in the art. If this is done,

two strings are required. If single only no phase current is available, only one string 'may be used or two strings in parallel or 1n series with each other. n

The muflles of hardening furnaces are as a rule closed at one end..- 'lhe top and bottom 'of heat but not of the furnace, as 1t reasons to arrange l to utilize three-1 1921. Serial No. 449,388.

neath the bottom side. The strings may be.

directly joined behind the end wall of the in ullie and two-phase-,or single phase cui'- rent may be employed. lf the muie is lto be Aopenat both ends, the strings can not have a common oontactbehind the end wall,.

but in such a ease the strings may be connected together;by means of a ring of re.A

sistance material .surrounding the muflie a *short distance Yfrom the end.

l; Themuiliemay be used in a vertical as, .well as 1n a horizontalI position.

.If .the muffle is to be used as a Crucible for meltin pur oses,th e furnace may` be arran e tofti-t in the usual way so as to faci ltate dischargin of the contents.

Openings should eprovided at suitable places, permitting inspection and renewal of theresistance material, when required.

The material ,of which the crucible or muffle is-'tobe madashould be @good @HdM-t0".

l electric current. The meltln point should for obvious reasons be as hlg as possible. Consequently bonded carborundum, ,carbofrax C, silica or pos- .Slblya-high ,grade fire clay would be well suitablefor ,the purpose.

According; to this invention it would be possible toconstruct a furnace havinga plurality of crucibles arranged in a line parallel to each other and separated from each ,other by means of layers of resistance material. It is obvious that in such a case lit 'is-,not necessary, that the cross section of f the crucibles is flattened as the circular form 1f certain precautions are observed so as to separate and insulate the heating resistances from each other. A-furnace having a plurality of crucibles heated according' to the principles disclosed in this specification should prove very suitable for solving several metallurgical problems involving the generation of heat without fuel. The furnace should. thus, be,well adapted for making iron sponge, for reducing tin, zinc, copper and other metals from their combinations with oxygen or other elements.

In the accompanying drawino several furnaces in modified forms are illustrated. Figure 1 -a vertical cross section on the may also be used,

line X-X. Fig. 2 and Fig. 2 is partly a vertical cross"` section on line1 l1 -y Fi nl, partly an e'nd View. Said giures ilh'i'strate a furnace having a muiie with rectangular or oval cross section open at one end The furnace may be used in both horizontal and vertical position. Fig. 3 is a verticaleross section of a furnace having a plurality of horizontal inuilies aliinged above e'ach other. The same figuremmy represent a horizontal cross section of a furnace haring a plurality of iietical mufiles ringed in a line one after the other; The' ni'liie. inl Fig. 3 may be open at only one or .at b'oth ends. Fig. 4 is`l a cross4 section o f a fu'riiiicev havin' -a circular inuilie, h'e'ted on two s'ides by 'arate rsistances'. 5` is a rss section 0`f a furnace having :i mulilefoftrin 'lar cross section, He'ted by mans of esisganc' units correspon'ng to each side'. Fi is' avvertical cross section of a furna'ce in Which a plurality of niuiiiles plac'l s'id by side are lieted by mns of a stin" 'f rsistance material below and on' top' o thecuibles. The section is taken at z-z in 7, which is a cross section at 'vl-"u in' Fig. 6L This figure n'i'a'y also represent horizontal cross Section at z`-z' i'ii Fig. 7.y In this case' the muiiies are standing upright with' their bottoms dzonn. The' space' between' the r'nufiies 'n'd the furnace walls is completely filled withrsistance h'lteiliil.

Similar Vnu'r'nerals refer to similar parts throughout the severalV v'ews.

In Figs. 1 and' 2 a a muiiie is indicated with 1. Between the' furnace will aand the4v Inu'fiie resistance material is i'n'd'icted with 3. This resistance d''' not S'lllbud the munie an au aids-,tut only an' a pir-rief the fiat surfaces' being in contact with the muiiie on the top s'i'd', but not necessarily touching the lower side' o`f the 'rhume'. The resistance passs also' behind the bottom' of the mullie indicated in Fig. 1.` Electric current is admitted to th'e heatin' resist- :ince by meanls'oi contacts 4, f. i.. carbon projecting into the resistance. If tiro-phase current is to be used, thev contact behind the bottoni of the lii'uflie (to tlie'Y left in Fig. I) is to be connectedI to the c'olnm'on p'oint of the tryo phases. If single phase 'current is to be used the said Contact nifty be 4oniittd butv it may also be used for connecting the i'i'p'er and lower rsistances in parallel with each other. In'lthis' way a' certain' regulation -of the generation of heat may be obtained. The space between the furnace niall and theV .In e should be closed' by doo'r's at either endI of the furnace prmittin' t e inspection' ofthe heating chambe'ran also refilling of tlie resistance mateil2 Wli''ri required. To facilitate this the furnace may be raised to an upright positioti1 the resistance material being simply dropped into the heating chamber. The

contacts 4 should he watcrminled in suitable mannerz if required.

In Fig. 3 a plurality of inufiies l hare heen arranged above each other inside olf a furnace wall 2.and separated h v means of iay'rs of resistance material 2i. The mufilesare preferably7 lattened or oral in cross section. Electric current is admitted in any preferred manner by means of contacts 4 projecting into the heating resistance. The type of furnace illustrated by Fig. 3 offers certain advantages when, the Hoor space is limited. The thermal efficiency also is improved as the heat-loosing surface is considerably reduced in comparison with the Volume of the muilies. If so desired it is also p'ossibleto arrange the muiiies .of this type in vertical position. Fig. 3 would then represent a horizontal cross section.

In Fig. 4 a modified form of the furnace Figs. l and 2 is illustrated. The furnace 2 in this case isprovided with a cylindrical mufiie Lheated by means of tworesis'tances 3,- one on each side and separated from each other by' means of an insulating Wall 6. Conta'cts tare provid-ed for admitting electric current to the resistance. According to Fig. 5 the munie of a furnace built as indicated in Fig. 4 may be modified by giving it a' triangular cross section. To each side of the Inutile corresponds a strip of resistance running alongside the muiiie. The three.re sistances may be conveniently connected to a three-phase power net. The resistances niy be connected in star or delta' as desired. t

In Figs. 6 and 7 another modificatioiris illustratedgirhich is provided with a plurality o'f miifiies .l arranged side by iside ina furnace 2 and adjoining cach other. ,The heat is generated by means of a resistance on the to side of and another resistance underneat the munies. The resistance in this modified forni is running crosswise. to the lengthl of each separate. muliie but lengthwise if all individual' muliles are considered as a unit.. The resistances are provided with contacts 4 for admittingr current in any preferred manner.

It is obvious thatboth direct and' alternating current may be used in' ,furnaces as described in this specification. The furnaces are independent up to a certain limit ofthe voltage available and also of the frequency.

Having now fully described. my invention, I claim:

1'. Inv an electric furnace the combination of an elongated Crucible with a plurality of strings of carbonaceous resistance material located lengthwise a'long the Crucible, electrically insulating material separating the strings from each other and meansfor conducting electric energy to the resistances.

2. In an electric furnacethe combination of an elongated Crucible with a plurality 0f strings of carbonaceous resistance material located lengthwise along the Crucible, electrically (insulating material separating the strings from each other a common connection between the strings at one end of the Crucible and means for conducting electric energy to the opposite ends of the strings.

Signed at Stockholm in the county of Stockholms Lan and State of Sweden this 12th day of February, A. D. 1921.

IVAR RENNERFELT.

Witnesses:

Imaz SwmNsoN, HUBERT BENSON. 

